Weather in Pennsylvania has impeded search efforts for a 9-month-old boy and his 2-year-old sister, who have been missing for several days after being swept away during flash flooding in the Philadelphia suburbs.

Five people — including the children's mother — died on a flooded roadway in eastern Pennsylvania on Saturday evening. In the days since, rescue workers have searched the flood zone more than a dozen times, the Upper Makefield Township Police Department said. 

"Regrettably, despite these resources and the tremendous effort put forth by our search and rescue personnel, we have not been able bring Mattie and Conrad home to their loving family," police wrote on Facebook. 

The Charleston, South Carolina, family was driving when they got caught in flash flooding. The missing children's father, grandmother and 4-year-old brother were also in the car at the time, and survived the flooding, officials said.

The flash flooding occurred about 30 minutes north of Philadelphia by car and just under a mile from Houghs Creek, a tributary in the Delaware River. Police said dive teams have been unable to assist in the search because of fog and expected storms.

"This is extremely heartbreaking to us, to the family, and to all of you," police said Thursday on Facebook.

K9 teams and officers from the Philadelphia Police Department have assisted in the search, officials said. Rescue workers have also been moving large debris piles to help the K9 teams in their search efforts. 

President Joe Biden, who was in Philadelphia on Thursday for an unrelated event, addressed the deadly flooding. 

"I want to say we're praying for those who lost their lives in the flooding in Bucks County. The idea that there's not global warming, I think can't be denied by anybody anymore," he said. "Anyway, we're grateful for the first responders who continue to look for a 2-year-old, Mattie, and her baby brother, Conrad. By the grace of God, maybe something will come of it."

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• Pennsylvania

Aliza Chasan

Aliza Chasan is a digital producer at 60 Minutes and CBS News.

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